A fiber optic gyroscope (FOG) uses the interference of light to measure angular velocity. Rotation is sensed in a FOG with a large coil of optical fiber forming a Sagnac interferometer. To measure rotation, two light beams are introduced into the coil in opposite directions by an electro-optic modulating device such as an integrated optical circuit (IOC). If the coil is undergoing a rotation, then the beam traveling in the direction of rotation will experience a longer path to the other end of the fiber than the beam traveling against the rotation. This is known as the Sagnac effect. As the beams exit the fiber they are combined in the IOC, and the phase shift between the counter-rotating beams due to the Sagnac effect and modulation in the IOC causes the beams to interfere, resulting in a combined beam, the intensity and phase of which depends on the angular velocity of the coil.